This invention relates to a suspension device of a leaf spring type for an automobile, and more particularly to a FRP (fiber reinforced plastics) leaf spring.
Conventionally, an automotive suspension device using a leaf spring includes a metal center pin 20 at a longitudinally central portion of a leaf spring 12 as shown in FIG. 6, so as to ensure center positioning and prevent forward and rearward movements of the leaf spring body due to a forward and a rearward force acting thereon upon installation of the leaf spring to an axle housing 21. Another suspension device using a FRP leaf spring for purposes of lightening of weight includes the center pin embedded into the leaf spring upon molding thereof, or inserted into a through-hole formed through the leaf spring after molding thereof, in the same manner as with the suspension device using a metal leaf spring. In another way, as shown in FIG. 10, two center pins 70 having flanges 70a are bonded at the flange sides to an upper and a lower surface of a leaf spring 62. However, as strength of the FRP leaf spring is smaller than that of a steel spring, fatigue life of the FRP leaf spring is disadvantageously decreased because of the forward and the rearward force applied to the FRP leaf spring, and stress concentration at the portion of the FRP leaf spring around the center pin which stress concentration is created by up-and-down motion of the leaf spring.